A known apparatus for a power seat is disclosed in JP2001-277909A. According to the apparatus for the power seat of JP2001-277909A, a pair of upper rails for supporting a seat is arranged at a pair of lower rails fixed at a vehicle floor so as to be relatively slidable. The pair of upper rails is moved relative to the pair of lower rails by means of a driving force of a slide motor in a front-rear direction of a vehicle, thereby changing a position of the seat in the front-rear direction of the vehicle.
Further, the apparatus for the power seat includes a sensor that outputs a single pulse in accordance with a rotation of a motor (i.e., a sensor having only one hall element). A position of the seat in the front-rear direction of the vehicle is determined on the basis of a counted pulse, and then, the position of the seat is memorized. A rotational direction of the motor is judged on the basis of an output direction (an electrical characteristic) of the motor. In a case where the rotation of the motor is stopped when the seat reaches an end of a movable range, the motor becomes a mechanically-locked state (a motor-locked state), and the driving (an output) of the motor is stopped. At that time, the motor may be driven in a reverse direction (a reverse rotation) due to a reaction force of a load-applied side. Consequently, a difference may be generated between an actual position of the seat in the front-rear direction of the vehicle and a position of the seat determined and memorized by the apparatus. Accordingly, in order to restrict the generation of the difference, according to the apparatus for the power seat of JP2001-277909A, whether the motor is in the mechanically-locked state or not is determined, and a pulse that is outputted after the mechanically-locked state of the motor is determined is determined to correspond to the reverse rotation of the motor, thereby correctly determining the position of the seat in the front-rear direction of the vehicle.
However, according to the apparatus for the power seat of JP2001-277909A, in a case where the driving of the motor, which has been in the mechanically-locked state, is started in response to an operation of an operational switch, and subsequently the driving motor is stopped before the mechanically-locked state of the motor is determined, the pulse outputted from the sensor after the stopping of the driving of the motor is determined to correspond to a forward direction of the motor (i.e., a direction corresponding to a last output direction of the motor, or a rotation indicated by the operational switch). As a result, a difference may be generated between an actual position of the seat in the front-rear direction of the vehicle and a position of the seat determined and memorized by the apparatus. Furthermore, such operation may be repeatedly performed. Therefore, the difference may be accumulated. Accordingly, in a case where a movement of the seat is controlled on the basis of the memorized position of the seat in the front-rear direction of the vehicle (for example, in a case where the seat is controlled to return to the memorized position), an accurate operation may become difficult.
A need thus exists for an apparatus for a power seat, which is not susceptible to the drawback mentioned above.